This invention relates to the field of devices, systems and methods for testing electronic circuits by applying and measuring electrical signals, and more particularly to devices, systems and methods for supporting automated test equipment (ATE). The ensure proper functionality and reliability, manufacturers typically test wafers, memory devices (such as DRAM and Flash) or other integrated circuits (ICs) at various stages of manufacturing and before shipping to customers.
In recent years, device testers have undergone many changes in order to handle tester of denser, faster and higher volumes of devices. Speed and density have increased by multiple orders of magnitude with testers changing to keep up with the devices. However, as speeds increased, signal path length has become a critical issue. Minimizing path length to achieve high speeds has led to miniaturization by a factor of over 1000 in less than five years. As test electronics is forced to ever greater speeds and densities, one major limitation is the removal of the internal heat generated by the tester. In prior generations of automated test equipment, air cooling was sufficient. However, recent generations of machines are too fast and densely packed for air cooling to be practical and water cooling has been employed for many areas of ATE machines.
A typical tester 100 is illustrated in FIG. 1 with a system bay or upright support rack 140, which houses the support devices for the test head 110, a cooling unit, power supplies and controller for the test electronics. Large bundles of electrical cables and cooling water hoses 160 connect the system bay 140 to the test head 110. The test head 110 is a relatively small enclosure that houses all the tester electronics. The actual signal generation and analysis are performed in the test head 110. Attached to the test head 110 is an interface 120, which is an electromechanical assembly that is essentially a very large connector that permits various probe cards 150 to be attached to the test head 110. The probe card 150 contacts a wafer (not shown) under test and makes electrical contact with the metallic pads on the wafer's surface.
As shown in FIGS. 2 and 3, a typical probe card 150 has an array of contacts (not shown) that make temporary electrical contact with the device under test (not shown). Generally these contacts are some type of spring contact that contacts metallic pads on the device. There are many companies manufacturing probe cards, each with different contact construction and design. The common denominator of any probe card to be interfaced with a particular ATE tester, is a set of proprietary contacts 105 that interface the probe card 150 to the test head 110 via proprietary connections 108 on the interface 120 and the overall dimensions of the probe card 150, which are governed by the tester interface 120 geometry and limitations of the device prober (not shown).
As new and cost effective solutions for the ATE industry are developed, functionality is being added to many devices that heretofore were totally passive, necessitating novel approaches to cooling. One problem in the testing of at least one type of Flash memory (NOR) at the wafer level is that the resources of the tester are too expensive to devote entirely to one IC. Therefore, a means of sharing the tester resources among many devices under test is being developed, resulting in a type of multiplexing scheme, in which tester resources are dynamically switched among many die. Due to the timing accuracy required, using current technology, this switching must take place a very short distance from the die. Currently, due to interconnect limitations and signal path considerations, to accomplish this necessitates putting active components on the probe card 150. One can envision many other types of circuits that would be useful to locate on a probe card 150, for timing or precision measuring considerations, etc.
However, one limitation to mounting active circuitry on the probe card 150 is the heat generated by the devices. Some designs using active signal conditioning dissipate substantial amounts of power, so a probe card may dissipate upwards to a half a kilowatt or more. Heat inputs of this magnitude to the interior of the prober cannot be tolerated, so some method of active cooling to remove heat from the probe card 150 is necessary moving forward.
Although many current ATE testers make extensive use of water cooling, this method of cooling the probe card may be problematic. Water blocks are used in ATE testers to which various PCBs are attached in order to transfer heat into the water. One problem with using this method to cool the probe card 150 is due to potential leakage or spillage of the cooling fluid when installing or removing the probe card 150 from the interface 120. Probers (not shown) are made so that a probe card is inserted into the prober, then internal automation (not shown) mates the probe card 150 to the interface 120 and latches it. The electrical connections in present generations of testers are often made using pneumatically activated connectors 108, which occurs after the probe card 150 is latched to the tester interface 120.
A water cooled probe card 150 would need to make and break a connection to the water path using automated quick disconnects. All such fittings leak a slight amount when breaking the connections. This would not be acceptable in the confines of current probers, which are very sensitive mechanical systems that position wafers with accuracies in the micron range. The option of removing the test head 110 from the prober to change probe cards 150 is not feasible, because this is a manual operation. Since probe cards 150 may cost more than one hundred thousand dollars, they are always handled using automation.
Therefore, there is a need to cool electronic devices and active circuit elements on probe cards or on the interface more reliably than traditional water cooling techniques.